1. Field of Invention
The present invention relates generally to the modification of engine valve lift for producing an engine valve event in an internal combustion engine, particularly to engine braking apparatus and methods for converting an internal combustion engine from a normal engine operation to an engine braking operation.
2. Prior Art
It is well known in the art to employ an internal combustion engine as brake means by, in effect, converting the engine temporarily into a compressor. It is also well known that such conversion may be carried out by cutting off the fuel and opening the exhaust valve(s) at or near the end of the compression stroke of the engine piston. By allowing compressed gas (typically, air) to be released, energy absorbed by the engine to compress the gas during the compression stroke is not returned to the engine piston during the subsequent expansion or “power” stroke, but dissipated through the exhaust and radiator systems of the engine. The net result is an effective braking of the engine.
An engine brake is desirable for an internal combustion engine, particularly for a compression ignition type engine, also known as a diesel engine. Such engine offers substantially no braking when it is rotated through the drive shaft by the inertia and mass of a forward moving vehicle. As vehicle design and technology have advanced, its hauling capacity has increased, while at the same time rolling and wind resistances have decreased. Accordingly, there is a heightened braking need for a diesel-powered vehicle. While the normal drum or disc type wheel brakes of the vehicle are capable of absorbing a large amount of energy over a short period of time, their repeated use, for example, when operating in hilly terrain, could cause brake overheating and failure. The use of an engine brake will substantially reduce the use of the wheel brakes, minimize their wear, and obviate the danger of accidents resulting from brake failure.
There are different types of engine brakes. Typically, an engine braking operation is achieved by adding an auxiliary engine valve event called an engine braking event to the engine valve event for the normal engine operation. Depending on how the engine valve event is produced, an engine brake can be defined as:                (a) Type I engine brake—the engine braking event is produced by importing motions from a neighboring cam, which generates the so called Jake brake;        (b) Type II engine brake—the engine braking event is produced by altering existing cam profile, which generates a lost motion type engine brake;        (c) Type III engine brake—the engine braking event is produced by using a dedicated cam for engine braking, which generates a dedicated cam (rocker) brake;        (d) Type IV engine brake—the engine braking event is produced by modifying the existing valve lift, which normally generates a bleeder type engine brake; and        (e) Type V engine brake—the engine braking event is produced by using a dedicated valve train for engine braking, which generates a dedicated valve (the fifth valve) engine brake.        
The engine brake can also be divided into two big categories, i.e., the compression release engine brake (CREB) and the bleeder type engine brake (BTEB).
Compression Release Engine Brake (CREB)
Conventional compression release engine brakes (CREB) open the exhaust valve(s) at or near the end of the compression stroke of the engine piston. They typically include hydraulic circuits for transmitting a mechanical input to the exhaust valve(s) to be opened. Such hydraulic circuits typically include a master piston which is reciprocated in a master piston bore by a mechanical input from the engine, such as the pivoting movement of the fuel injector rocker arm. Hydraulic fluid in the circuit transmits the motion of the master piston to a slave piston in the circuit, which in turn, reciprocates in a slave piston bore in response to the flow of hydraulic fluid in the circuit. The slave piston acts either directly or indirectly on the exhaust valve(s) to be opened during the engine braking operation. This is a Type I engine brake.
An example of a prior art CREB is provided by the disclosure of Cummins, U.S. Pat. No. 3,220,392 (“the '392 patent”), which is hereby incorporated by reference. Engine braking systems based on the '392 patent have enjoyed great commercial success. However, the prior art engine braking systems have certain inherent disadvantages that have limited their application to primarily larger vehicles such as heavy duty trucks (and typically, on engines having a displacement of about 10 liters or more), and their retrofit to existing engines is largely impossible without substantial modification of the engine cylinder head.
One of the disadvantages associated with the conventional prior art CREB system is due to the fact that the load from engine braking is supported by the engine components. Because the engine braking load is much higher than the normal engine operation load, many parts of the engine, such as the rocker arm, the push tube, the cam, etc. must be modified to accommodate the engine braking system. Thus, the overall weight, height, and cost of using the prior art CREB system are likely to be excessive, and limit its commercial application.
Another disadvantage associated with the conventional prior art CREB system is the high and unique noise generated by the releasing of high-pressure gas or “blow down” through the exhaust valve(s) during the compression stroke, near the top dead center position of the engine piston.
Additional disadvantages of the prior art systems reside in their relative complexity and the necessity for using precision components because they require accurate timing and hydraulic actuators capable of opening the exhaust valves precisely when required. Thus they may be comparatively expensive and difficult or impossible to install on certain engines.
Yet another disadvantage associated with the conventional prior art CREB system of hydraulic type is the compliance of the braking system, which may cause the braking valve lift to collapse at the peak braking load (near compression top dead center (TDC) of the engine piston) and further increase the braking load. The large reduction of braking valve lift due to compliance will reduce the braking performance and excessive braking load may cause engine damage.
Bleeder Type Engine Brake (BTEB)
The operation of a bleeder type engine brake (BTEB) has also long been known. During bleeder type engine braking, in addition to the normal exhaust valve lift, the exhaust valve(s) may be held slightly open during a portion of the cycle (partial-cycle bleeder brake) or open continuously throughout the non-exhaust strokes (intake stroke, compression stroke, and expansion or power stroke) (full-cycle bleeder brake). The primary difference between a partial-cycle bleeder brake and a full-cycle bleeder brake is that the former does not have exhaust valve lift during most of the intake stroke. An example of BTEB system and method is provided by the disclosure of the present inventor, U.S. Pat. No. 6,594,996, which is hereby incorporated by reference.
Usually, the initial opening of the braking valve(s) in a bleeder braking operation is far in advance of the compression TDC and then the braking valve lift is held constant for a period of time. As such, a BTEB may require much lower force to open the valve(s) due to early valve actuation, and generates less noise due to continuous bleeding instead of the rapid blow down of the CREB. Moreover, a BTEB often requires fewer components and can be manufactured at a lower cost. Thus, a BTEB can overcome some of the disadvantages of the CREB. Indeed, the BTEB systems have achieved certain commercial success, especially in the application to smaller vehicles, such as the middle and light duty trucks (and typically, on engines having a displacement of less than 10 liters). Following are some BTEB systems that are currently on the market.
(a) BTEB Operated by Rocker Arm with Eccentric Shift
U.S. Pat. No. 5,335,636 discloses a bleeder type engine brake (BTEB) system wherein the pivot center of the engine exhaust rocker arm is displaced or shifted in a downward direction by an eccentric that is connected to a hydraulic piston/actuator by a level arm. The displacement or shift of the rocker arm pivot center causes the exhaust valves to open during braking operation of the engine to create a partial cycle bleeder braking event. This is a Type IV engine brake.
The BTEB system of the type described above requires an extra mechanical component between the hydraulic piston or actuator and the rocker arm. The system also requires intermediate arms, a second rocker arm eccentric bore, features on the small end of the actuation/pivot arm and features on the mechanical actuation end of the piston. These parts and features all add cost and complexity, and reduce system reliability. Also, the system is integrated into the engine exhaust valve train. Load from engine braking by opening both exhaust valves is so high that other parts of the engine, such as the rocker arm, the push tube, the cam, etc. must be redesigned. Finally, such type of engine brakes cannot be retrofitted into existing engines.
(b) BTEB Operated by a Dedicated Engine Braking Valve
U.S. Pat. No. 5,168,848 discloses a bleeder type engine brake (BTEB) system that has an extra exhaust valve in addition to the normal engine exhaust valve(s). The extra exhaust valve is dedicated to engine braking and opened exclusively during braking operation of the engine. The dedicated engine braking valve is actuated by pneumatic or hydraulic means and held open to create a full cycle bleeder braking event. This is a Type V engine brake.
The BTEB system of the type described above is integrated into the cylinder head of the engine, thereby substantially conditioning its design and manufacture. The engine braking device is therefore dedicated to a particular type of engine. Moreover, the introduction of the extra exhaust valve creates an extra pocket in the combustion chamber, which increases engine emission. Also, such type of engine brakes can not be used in existing engines.
(c) BTEB Operated by Engine Valve Floating
U.S. Pat. No. 5,692,469 and U.S. Pat. No. 7,013,867 disclose a bleeder type engine brake (BTEB) system for engines with one and two exhaust valves per cylinder. The BTEB system includes a throttling device (also known as an exhaust brake) capable of raising exhaust pressure high enough to cause each exhaust valve to float near the end of each intake stroke. In this intermediate opening or floating of the exhaust valve, it is possible to intervene with the braking device so that the exhaust valve, which is about to close after the intermediate opening, is intercepted by a control piston charged with oil pressure and prevented from closing to create a partial cycle bleeder braking event. This is a Type IV engine brake.
The BTEB system of the type described above may not be reliable because it depends on the intermediate opening or floating of the braking exhaust valve, which is not consistent, both in timing and magnitude. As is well known in the art, exhaust valve floating is highly engine speed dependent and affected by the quality and control of the exhaust brake, and also the design of the exhaust manifold. There may be not enough or none valve floating for the actuation of the engine braking device at middle and low engine speeds when the engine brake is highly demanded since the engine is mostly driving at such speeds. Again, such type of engine brakes may not be able to retrofit into existing engines.
(d) BTEB Operated by High-Pressure Oil
U.S. Pat. No. 6,866,017 and U.S. Pat. No. 6,779,506 disclose a bleeder type engine brake (BTEB) that is actuated and controlled by high-pressure hydraulic fluid, or oil. The hydraulic fluid is supplied from a hydraulic rail, or oil rail, to a respective fuel injector at each engine cylinder to act on a piston in the fuel injector to force a charge of fuel into the respective combustion chamber during normal engine operation. A hydraulic actuator in the engine brake uses the already available high-pressure oil to actuate and hold one exhaust valve open to create a full cycle bleeder braking event. This is also a Type IV engine brake.
The BTEB system of the type described above is dedicated to a particular type of engine that has high-pressure oil rail (source), which greatly limits its application. Sophisticated electronic control is needed to eliminate excessive oscillations of the shared common high pressure source and to ensure a smooth transition between engine braking operation and normal engine operation. Also, such type of engine brakes cannot be retrofitted into existing engines.
It is clear from the above description that the prior-art engine brake systems have one or more of the following drawbacks:
(a) The system can only be installed on a particular type of engines;
(b) The system cannot be retrofitted to existing engines;
(c) The engine braking load is carried by the engine components;
(d) The system installment needs redesign of the engine or engine components;
(e) The system has too many components and is too complex;
(f) The system increases the manufacturing tolerance requirements and is too costly;
(g) The system is not reliable and only work at certain engine speeds; and
(h) The system affects normal engine performance (emission, oil rail pressure, etc.).